A relay station acts as an intermediary between a base station and a mobile station by communicating with the base station and mobile station. In addition, the relay station may act as an intermediary between a base station and a second relay station by communicating with the base station and the second relay station or between a second relay station and a mobile station by communicating with the second relay station and the mobile station. To avoid self interference between a transmitter and receiver in the relay station, usually the relay station can not receive data and transmit data simultaneously in the same system operation band. Different time slots are allocated to the links from base station to relay station, from mobile station to relay station, or from relay station to relay station for both frequency division duplexing (FDD) and time division duplexing (TDD).
Some shortcomings of such a half-duplex FDD or TDD base relay transmission are:
1. a reduced efficiency of the system;
2. modification of frame structure in necessary to accommodate the half duplex nature of the transmissions;
3. difficulty in supporting synchronous HARQ; and
4. difficulty in monitoring all mobile stations.